Gas-generating agent for air bag

ABSTRACT

The present invention provides a gas generating agent for an air bag including a fuel component of nitrogenous organic compound and an oxidizing agent as its major components, to which at least one metal nitride or metal carbide that is allowed to react with a metallic component contained in the fuel component or the oxidizing agent to form slag is added, thus providing the effects of: solving the slag collecting problem which stands in the way of commercially practicing the nitrogenous organic compound base fuels; promoting the size reduction of the gas generator through the full use of high rate of gasification of the nitrogenous organic compound base fuels; and providing a gas generating agent molded member which is strong and stable with age by improving heat resistant properties and formability of the nitrogenous organic compound base fuels which are poor compared with the metallic compound azide of an inorganic matter.

TECHNICAL FIELD

The present invention relates to a gas generating agent for air bags,and particularly, to a novel gas generating agent having excellentcapabilities of collecting slag and generating reduced harmful gas.

BACKGROUND ART

An airbag system, which is a rider protecting system, has been widelyadopted in recent years for improving safety of the riders in anautomobile. The airbag system operates on the principle that a gasgenerator is operated under control of signals from a sensor detecting acollision, to inflate an airbag between riders and an car body. The gasgenerator is required to have a function to produce a required andsufficient amount of clean gas containing no harmful gas in a shorttime.

On the other hand, the gas generating agents are press-formed into apellet form for stability to the burning, and the pellets and equivalentare required to maintain their initial flammability characteristics overa long time even under various harsh environments. In the event that thepellets deform or decrease in strength due to deterioration with age,change of environments and the like, the flammability of the explosivecompositions will exhibit at an abnormally earlier time than the initialflammability, so there is a fear that the airbag or the gas generatoritself may be broken with the abnormal combustion in case of acollision, to fail in accomplishing the aim of protecting the riders oroven cause them injury. To satisfy those required functions, gasgenerating agents containing metallic compound azide, such as sodiumazide and potassium azide, as their major component have been usedhitherto. These known gas generating agents are widely used in terms oftheir advantages that they are burnt momentarily; that the component ofcombustion gas is substantially nitrogen gas only, so that no harmfulgas such as CO (carbon monoxide) or NOx (nitrogen oxide) is produced;and that since the burning velocity is little influenced by theenvironment or the structure of the gas generator, it is easy to designthe gas generator. However, the azide produced by contact of themetallic compound azide and the heavy metal has the nature of beingeasily exploded by impact and friction, so that it must be handled withthe greatest possible caution. Further, the metallic compound azideitself is a harmful material and further has a notable disadvantage thatit can decompose in the presence of water and acid to produce harmfulgas.

Accordingly, as the substitution of metallic compound azide, gasgenerating agents containing tetrazoles, azodicarbonamides and othernitrogenous organic compounds as fuel components have been proposed by,for example, Japanese Laid-open Patent Publications No. Hei2(1990)-225159, No. Hei 2(1990)-225389, No. Hei 3(1991)-20888, No. Hei5(1993)-213687, No. Hei 6(1994)-80492, No. Hei 6(1994)-239684 and No.Hei 6(1994)-298587. The tetrazoles in particular have a high proportionof atoms of nitrogen in their molecular structure and inherently havethe function to suppress the production of CO such that production of COcan be suppressed, so that almost no CO is produced in the combustiongas, as in the case of the metallic compound azide. Besides, thetetrazoles are superior to the abovesaid metallic compound azide in farless danger and toxicity.

Chlorates, such as alkaline metals or alkaline earth metals,perchlorates or nitrates are generally used for oxidizing agents usingthe nitrogenous organic compounds as fuel to be burnt. The alkalinemetals or the alkaline earth metals produce oxides as a result of theburning reaction, and the oxides are harmful materials for a human bodyand environment such that they must be in the form of easily collectableslag to be collected in the gas generator so that they can be preventedfrom being released into the air bag. However, since many of the gasgenerating agents using the nitrogenous organic compounds as fuel to beburnt have the heat of combustion as high as 2,000-2,500 joule/g ormore, the gas generated becomes high in temperature and pressure. As aresult of this, the slag which is a by-product obtained in the burningof the gas generating agents increase in temperature and thus increasein flowability. In a conventional type of gas generator, a filter fittedtherein tends to reduce its slag collection efficiency. For increase ofthe slag collection efficiency, a method of increased number offiltering members being set in the filter to cool and solidify the slagmay be practical, but such a method has a disadvantage of increasing thesize of the gas generator, going against the trend toward the sizereduction and weight reduction of the gas generator.

Also, various methods of addition of slag forming agents have beenproposed for collecting the oxide of alkaline metal or alkaline earthmetal in the form of the slag to be easily collected in the filteringpart with efficiency. In these methods, silicon dioxide or aluminumoxide is in principle added as an acid substance or a neutral substanceeasily slag-reactable with the oxides which are basic substances. Theproposed methods are conceptually the same as the conventionalslag-forming method for the gas generating agent using metallic compoundazide as the fuel. The proposed method is the method in which silicateor aluminate is used as the oxide and is converted into a high-viscosityor high-melting, glassy substance, to collect the oxide as the slag.Japanese Laid-open Patent Publication No. Hei 4(1992)-265292, inparticular, discloses the method in which a low-temperature slag-formingsubstance as typified by silicon dioxide and a high-temperatureslag-forming forming agent (e.g. alkaline earth metal ortransition-metallic oxide) which produces a solid having a melting pointclose to or more than the reaction temperature are both added to allowhigh-melting particles, which are solid matters produced by burningreaction, to react with low-temperature slag-forming agents in moltencondition and the resultant particles are fused among themselves toimprove the collecting efficiency.

However, the addition of the large amounts of substances that do notcontribute to the generation of gas causes reduction of a relativeproportion of the fuel components of the gas generating components, sothat a rate of gasification is high, as compared with the known metalliccompound azide, so that the advantage of the nitrogenous organiccompound base fuels of holding promise of reducing the size of the gasgenerator may be impaired.

It is the primary object of the invention to solve the slag collectingproblem which stands in the way of commercially practicing thenitrogenous organic compound base fuels. It is the secondary object ofthe invention to promote the size reduction of the gas generator throughthe full use of high rate of gasification of the nitrogenous organiccompound base fuels. Further, it is the tertiary object of the inventionto provide a gas generating agent molded member which is strong andstable with age by improving heat resistant properties and formabilityof the nitrogenous organic compound base fuels which are poor comparedwith the metallic compound azide of an inorganic matter.

DISCLOSURE OF THE INVENTION

The present invention provides means to solve these problems. A basicconstruction of the present invention comprises a fuel component ofnitrogenous organic compound and an oxidizing agent as its majorcomponents, to which at least one metal nitride or metal carbide isadded as a slag forming agent. The metal nitride and the metal carbideare allowed to react with a metallic component or an oxide thereofcontained in the fuel component or the oxidizing agent, to form slag.

Another basic construction of the gas generating agent comprises a fuelcomponent of nitrogenous organic compound and an oxidizing agent as itsmajor components, to which at least one metal nitride or metal carbideand a slag forming metallic component that is allowed to react with ametallic component of the metal nitride or the metal carbide or an oxidethereof, to form high-viscosity slag are added in the form of an element(a simple substance) or a compound.

Preferable as the metal nitride used in the present invention is atleast one metal nitride selected from the group consisting of siliconnitride, boron nitride, aluminum nitride, magnesium nitride, molybdenumnitride, tungsten nitride, calcium nitride, barium nitride, strontiumnitride, zinc nitride, sodium nitride, copper nitride, titanium nitride,manganese nitride, vanadium nitride, nickel nitride, cobalt nitride,iron nitride, zirconium nitride, chromium nitride, tantalum nitride,niobium nitride, cerium nitride, scandium nitride, yttrium nitride andgermanium nitride.

Also, preferable as the metal carbide is at least one metal carbideselected from the group consisting of silicon carbide, boron carbide,aluminum carbide, magnesium carbide, molybdenum carbide, tungstencarbide, calcium carbide, barium carbide, strontium carbide, zinccarbide, sodium carbide, copper carbide, titanium carbide, manganesecarbide, vanadium carbide, nickel carbide, cobalt carbide, iron carbide,zirconium carbide, chromium carbide, tantalum carbide, niobium carbide,cerium carbide, scandium carbide, yttrium carbide and germanium carbide.

Further, the metal nitride or the metal carbide may be pulverized intoimpalpable powder, adding thereto the fuel component and the oxidizingagent when pulverized, so that they can be allowed to have the functionas a consolidation preventing agent therefor. A common consolidationpreventing agent may be included as a consolidation preventing agent.

The slag forming metallic component that can be allowed to react withthe metal nitride or the metal carbide in a combustion process to formthe high-viscosity slag may be contained in the fuel component or theoxidizing agent or may alternatively be added in the form of an element(a simple substance) or another compound.

The slag forming metallic component includes at least one selected fromthe group consisting of silicon, boron, aluminum, alkaline metals,alkaline earth metals, transition metals and rare earth metals.

It is also a preferable form that the slag forming metallic component isadded in the form of hydrotalcites for which the general chemicalformula is as follows:

(M²⁺ _(1−x)M³⁺ _(x)(OH)₂ ^(x+)(A^(n−) _(x/n) .mH₂O)^(x−)

where

M²⁺ represents bivalent metal including Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺,Cu²⁺ and Zn²⁺;

M³⁺ represents trivalent metal including Al³⁺, Fe³⁺, Cr³⁺, Co³⁺ andIn³⁺;

A^(n−) represents an n-valence anion including OH⁻, F⁻, Cl⁻, NO₃ ⁻, CO₃²⁻, SO₄ ²⁻, Fe(CN)₆ ³⁻, CH₃COO⁻, oxalate ion and salicylate ion; and

0<x≦0.33.

Preferable as the hydrotalcites is synthetic hydrotalcite for which thechemical formula is Mg₆Al₂(OH)₁₆CO₃.4H₂O or pyroaurite for which thechemical formula is Mg₆Fe₂(OH)₁₆CO₃.4H₂O.

The nitrogenous organic compound includes at least one nitrogenousorganic compound selected from the group consisting of tetrazole,aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole,nitroaminotetrazole, triazole, nitroguanidine, aminoguanidine,triaminoguanidine nitrate, dicyanamido, dicyandiamido, carbohydrazide,hydrazocarbonamido, azodicarbonamide, oxamide and ammonium oxalate ortheir salts of alkaline metals, alkaline earth metals or transitionmetals. Of these nitrogenous organic compounds, tetrazole,aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole,nitroaminotetrazole, triazole are of preferable.

The oxidizing agent includes at least one oxidizing agent selected fromthe group consisting of nitrates of alkaline metal or alkaline earthmetal, chlorates of alkaline metal or alkaline earth metal, perchloratesof alkaline metal or alkaline earth metal and ammonium nitrates.

It is also preferable that at least one water-soluble polymer compoundselected from the group consisting of polyvinyl alcohol, polypropyleneglycol, polyvinyl ether, polymaleic copolymers, polyethylene imide,polyvinyl pyrrolidone, polyacrylamide, sodium polyacrylate and ammoniumpolyacrylate is added to the gas generating agent composition as aformability modifying agent.

It is also preferable that at least one lubricant selected from thegroup consisting of stearic acid, zinc stearate, magnesium stearate,calcium stearate, aluminum stearate, molybdenum disulfide and graphiteis added to the gas generating agent composition.

The following can be cited as preferable examples of the gas generatingagent composition.

{circle around (1)} A gas generating agent composition comprising 20 to50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and0.5 to 20 weight % silicon nitride.

{circle around (2)} A gas generating agent composition comprising 20 to50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; 0.5to 20 weight % silicon nitride; and 2 to 10 weight % synthetichydrotalcite.

{circle around (3)} A gas generating agent composition comprising 20 to50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and0.5 to 20 weight % silicon carbide.

{circle around (4)} A gas generating agent composition comprising 20 to50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; 0.5to 20 weight % silicon carbide; and 2 to 10 weight % synthetichydrotalcite.

{circle around (5)} A gas generating agent composition comprising 20 to50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and0.5 to 20 weight % silicon nitride, wherein a slag forming metalliccompound comprising at least one slag forming metal selected from thegroup consisting of aluminum, magnesium, yttrium, calcium, cerium andscandium is further mixed in the range of 1:9 to 9:1 in a ratio of thesilicon nitride to the slag forming metallic compound.

{circle around (6)} A gas generating agent composition comprising 20 to50 weight % 5-aminotetrazole; 30 to 70 weight % strontium nitrate; and0.5 to 20 weight % silicon carbide, wherein a slag forming metalliccompound comprising at least one slag forming metal selected from thegroup consisting of aluminum, magnesium, yttrium, calcium, cerium andscandium is further mixed in the range of 1:9 to 9:1 in a ratio of thesilicon carbide to the slag forming metallic compound.

{circle around (7)} The gas generating agent composition {circle around(5)}, {circle around (6)} wherein the slag forming metallic compound isat least one of oxide, hydroxide, nitride, carbide, carbonate andoxalate of the slag forming metal.

{circle around (8)} The gas generating agent composition {circle around(5)}, {circle around (6)} wherein the slag forming metallic compound issynthetic hydrotalcite.

As mentioned above, the present invention provides a gas generatingagent comprising nitrogenous organic compound as a fuel component and anoxidizing agent for burning it as its major components, to which eitheror both of metal nitride and metal carbide as the slag forming agent isadded, so that the metal nitride and the metal carbide can be allowed toreact with the metallic component or oxide thereof contained in thenitrogenous organic compound or the oxidizing agent, to form easilycollectable slag. This can provide the results that the fuel componentor the metal oxide derived from the oxidizing agent is allowed to reactwith the nitride or carbide in the process of combustion reaction, toform the high-viscosity slag to thereby produce the slag that can beeasily collected by the filtering part and that the nitrogen gasproduced by the burning of the metal nitride or the carbonic acid gasproduced by the burning of metal carbide can contribute to the inflationof the air bag, together with the nitrogen gas, carbonic acid gas andsteam produced by the burning of the nitrogenous organic compound of thefuel compound, and as such can contribute to reduction of the totalvolume of gas generating agents and reduction of size of the gasgenerator.

The slag forming metallic component that is allowed to react with themetal nitride or the metal carbide to form the high-viscosity slag inaccordance with the type of the metal nitride or the metal carbide maybe contained in the fuel component or the oxidizing agent or mayalternatively be added in the form of an element (a simple substance) orany independent compound, so that the high-viscosity slag can surely beproduced to provide improved slag collecting efficiency.

Particularly preferable gas generating agent compositions include a gasgenerating agent of system using 5-aminotetrazoles (5-ATZ) as the fuelcomponent and strontium nitrate as the oxidizing agent and addingthereto silicon nitride or silicon carbide; and those based on thissystem and using hydrotalcites both as the binder and the slag formingmetallic component or adding thereto the slag forming metallic componentthat is allowed to react with the metal nitride or the metal carbide toform the high-viscosity slag.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a gas generator used in anembodiment of the present invention;

FIG. 2 is a graph showing the relation between the time (t) in a 60liter tank test and the pressure (P) in a vessel; and

FIG. 3 is a diagram showing the result of the 60 liter tank test.

BEST MODE FOR CARRYING OUT THE INVENTION

The detailed description on the present invention will be given below.The gas generating agent of the present invention basically comprisesnitrogenous organic compound as a fuel component; an oxidizing agent forburning the nitrogenous organic compound; and metal nitride or metalcarbide used as a slag forming agent for improving slag collectingefficiencies.

Now, the nitrogenous organic compound used in the present invention willbe described first. In the gas generating agent of the presentinvention, the nitrogenous organic compound used as the fuel componentis a non-azide compound and also an organic compound containing nitrogenas a major atom in the structural formula. Specifically, at least onenitrogenous organic compound selected from the group consisting oftetrazole, aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole,nitroaminotetrazole, triazole, nitroguanidine, aminoguanidine,triaminoguanidine nitrate, dicyanamido, dicyandiamido, carbohydrazide,hydrazocarbonamido, azodicarbonamide, oxamide and ammonium oxalate ortheir salts of alkaline metals, alkaline earth metals, transition metalsor rare earth metals may be used. Of these nitrogenous organiccompounds, cyclic nitrogen compounds including tetrazoles, triazols orsalts thereof as listed above are preferable. Particularly preferableare tetrazoles having a high proportion of an atom of nitrogen in themolecular structure and having the structure of inherently restrainingproduction of harmful CO gas and high handling safety, or specifically,5-aminotetrazoles or metallic salts thereof as listed above. Preferably,the gas generating agent has the content of the fuel component of 20-50%(weight %, unless otherwise specified below). With the content of thefuel component of not more than 20%, a limited amount of gas isgenerated, so that an inflating failure of the air bag may possibly becaused. On the other hand, with the content of the fuel component inexcess of 50%, the added amount of oxidizing agent is relatively reducedto cause incomplete combustion and, as a result of this, there is apossible fear that a large amount of harmful CO gas may be generated.Further, in the extreme, there is a possible fear that unburned materialmay be produced.

In using the fuel component, the particle size is preferably adjusted inadvance by pulverizing the fuel component by addition of a small amountof consolidation preventing agent. In the present invention, it isparticular preferable that the fuel component is pulverized to 5-80 μmin the 50% average particle diameter of a reference number. Theconsolidation preventing agents which may then be added includeimpalpable powder of metal nitride or metal carbide as discussed lateror a usual consolidation preventing agent as combined therewith andfinely powdered. It is noted that the 50% average particle diameter of areference number is a method by which a particle size profile isexpressed with respect to a reference number: when the total number ofparticles is set to be 100, the particle size obtained when theparticles integrated from the smaller number reach 50 is called as the50% average particle diameter of a reference number.

Referring now to the oxidizing agent used in the gas generating agent ofthe present invention, it comprises at least one oxidizing agentselected from the group consisting of nitrates of alkaline metal oralkaline earth metal, chlorates of alkaline metal or alkaline earthmetal, perchlorates of alkaline metal or alkaline earth metal andammonium nitrates. Particularly preferable is strontium nitratecontaining a high-viscosity slag forming metallic component discussedlater. In using the oxidizing agent, the particle size is preferablyadjusted in advance by pulverizing the oxidizing agent by addition of asmall amount of consolidation preventing agent, as in the case of theabovesaid fuel component. In the present invention, it is particularpreferable that the oxidizing agent is pulverized to 5-80 μm in the 50%average particle diameter of the reference number. The consolidationpreventing agents which may then be added include impalpable powder ofmetal nitride or metal carbide as discussed later or a usualconsolidation preventing agent as combined therewith and finelypowdered. Preferably, the content of the oxidizing agent is in the rangeof 30-70% of the total gas generating agent. With the content of theoxidizing agent of less than 30%, an insufficient amount of oxygen issupplied, so that incomplete combustion may be caused to produce harmfulCO gas or, in the extreme, unburned material may be produced in thefuel, so that the required gas for inflating the air bag cannot besupplied to cause an inflating failure of the air bag. On the otherhand, with the content of the oxidizing agent in excess of 70%, there isa fear that shortages of fuel may be caused conversely, so that therequired gas for inflating the air bag cannot be supplied to cause aninflating failure of the air bag, as in the former case.

Referring now to the metal nitrides used in the gas generating agent ofthe present invention, it comprises at least one metal nitride selectedfrom the group consisting of silicon nitride (Si₃N₄), boron nitride(BN), aluminum nitride (AlN), magnesium nitride (Mg₃N₂), molybdenumnitride (MoN/Mo₂N), tungsten nitride (WN₂/W₂N,W₂N₃), calcium nitride(Ca₃N₂), barium nitride (Ba₃N₂), strontium nitride (Sr₃ N₂), zincnitride (Zn₃N₂), sodium nitride (Na₃N), copper nitride (Cu₃N), titaniumnitride (TiN), manganese nitride (Mn₄N), vanadium nitride (VN), nickelnitride (Ni₃N/Ni₃N₂), cobalt nitride (Co₂N/CO₂N/Co₃N₂), iron nitride(Fe₂N/Fe₃N/Fe₄N), zirconium nitride (ZrN), chromium nitride(CrN/Cr₂N),tantalum nitride (TaN), niobium nitride (NbN), cerium nitride(CeN), scandium nitride (ScN), yttrium nitride (YN) and germaniumnitride (Ge₃N₄).

Of the metal nitrides listed above, the sodium nitride (Na₃N) and thesodium azide (NaN₃) which have been used hitherto as the fuel of the gasgenerating agent are compounds fundamentally different from each other,and the sodium nitride is not included in the concept of the metalnitride defined in the present invention.

Of the these metal nitrides, silicon nitride, boron nitride, aluminumnitride, molybdenum nitride, tungsten nitride, titanium nitride,vanadium nitride, zirconium nitride, chromium nitride, tantalum nitrideand niobium nitride, which are called as fine ceramics and are used asheat-resistant materials which are thermally stable and high resistant,have the property of burning in high-temperature oxidizing atmospheres,as in the case of the other metal nitrides. In the present invention,both of the slag forming and the gas generation are simultaneouslyprovided through the use of their burning property. For example, in thecase of silicon nitride, nitrogen and silicate are produced byoxidization reaction with strontium nitrate as in the following formula(1):

2Si₃N₄+6Sr(NO₃)₂→3SrSiO₃+1ON₂+9O₂  (1)

The nitrogen gas thus generated are released in the air bag, togetherwith the nitrogen gas and carbon dioxide gas produced by the burning ofthe fuel components to be effectively used for inflating the air bag.The oxygen is used for the burning of the fuel components.

It is to be noted that the quantity of strontium nitrate used in the gasgenerating agent of the present invention is much more than the quantityconsumed by the reaction in accordance with the abovesaid formula (1).Accordingly, it seems that although the above said reaction is partiallyestablished, the strontium silicate represented in the following formula(3) is produced on a surface of strontium oxide produced by thedecomposition of strontium nitrate represented in the following formula(2):

2Sr(NO₃)₂→2SrO+2N₂+5O₂  (2)

SrO+SrSiO₃→Sr_(x)SiO_(y)  (3)

[where (x,y)=(2,4),(3,5); the coefficient of the reaction formula (3) isomitted.]

Also, while the strontium oxide produced by the decomposition ofstrontium nitrate, which is an oxide having a high melting point (2,430°C.), is produced in the form of a fine solid particle in the combustionprocess in the gas generator, various kinds of silicates having meltingpoints of about 1,600° C. are formed on surfaces of the particles by thereaction of the abovesaid formula (3). The silicates thus produced arein the molten state of high viscosity under environmental reactiontemperature, so the fine particles are fused together to aggregate,resulting in large particles to be easily collected in the filteringmembers in the gas generator.

In the case where the metal nitride is aluminum nitride (AlN), theformulas (1) and (3) are rewritten as follows. It is to be noted thatthe coefficient of the formula (5) is omitted.

2AlN+Sr(NO₃)₂→Sr(AlO₂)₂+2N₂+O₂  (4)

SrO+Sr(NO₃)₂→Sr_(x)(AlO₂)_(y)  (5)

Alminates thus produced also form high-viscosity slag layers on surfacesof the solid particles (SrO) to allow the fine slag particles to fuseand aggregate, to thereby form the slag that can be easily filtered bythe filters.

It is preferable that the added amount of the metal nitride is in therange of 0.5 to 20% of the total gas generating agent. With the metalnitride of not more than 0.5%, the slag collecting effects cannot beexpected, while on the other hand, with the metal nitride in excess of20%, the added amounts of fuel and oxidizing agent are limited, so thatthere presents a possible fear of shortage of gas generation andincomplete combustion. Preferably, their particle diameter is not morethan 5 μm, particularly not more than 1 μm, in the 50% average particlediameter of reference number, because the finer the particle diameter,the more the effects can be produced. Further, when a small amount offine particulate thereof is added to the fuel component or oxidizingagent component when pulverized, the small amount of fine particulatecan act as a consolidation preventing agent for those pulverizedcomponents and also can be dispersed uniformly in the oxidizing agentand the fuel, to ensure uniform reaction for the slag. When the metalnitride is used as the consolidation preventing agent, a usualconsolidation agent may be used in combination with it.

An example of the use of the metal nitride for the gas generating agentis disclosed by Japanese Patent Publication No. Hei 6(1994)-84274. Theknown gas generating agent uses aluminum nitride, boron nitride, siliconnitride or transition metal nitride as a substitute for the knownmetallic compound azide, using these metal nitrides as the so-calledfuel components. Thus, the prior art is fundamentally different inconcept from the present invention according to which the metal nitrideis used as the slag forming agent, to provide improved slag collectingcapabilities.

The metal carbides will now be described, which are used as the slagforming agent in the present invention, as in the case of the metalnitrides. The metal carbides used in the present invention include atleast one metal carbide selected from the group consisting of siliconcarbide (SiC), boron carbide (B₄C), aluminum carbide (Al₄C₃), magnesiumcarbide (MgC₂/Mg₂C₃), molybdenum carbide (MoC/Mo₂C), tungsten carbide(WC/W₂C), calcium carbide (CaC₂), barium carbide (BaC₂), strontiumcarbide (SrC₂), zinc carbide (ZnC₂), sodium carbide (Na₂C₂), coppercarbide (Cu₂C₂), titanium carbide (TiC), manganese carbide (Mn₃C),vanadium carbide (VC), nickel carbide (Ni₃C), cobalt carbide(Co₂C/CoC₂), iron carbide (Fe₂C/Fe₃C), zirconium carbide (ZrC), chromiumcarbide (Cr₃C₂/Cr₇C₃/Cr₂₃C₆), tantalum carbide (TaC), niobium carbide(NbC), cerium carbide (CeC₂), scandium carbide (ScC₂), yttrium carbide(YC₂) and germanium carbide (GeC).

Of these metal carbides, silicon carbide, boron carbide, molybdenumcarbide, tungsten carbide, titanium carbide, vanadium carbide, zirconiumcarbide, chromium carbide, tantalum carbide and niobium carbide, whichare called as fine ceramics and are used as heat-resistant materialswhich are thermally stable and high resistant, have the property ofburning in high-temperature oxidizing atmospheres, as in the case of theother metal carbides. In the present invention, both of the slag formingand the gas generation are simultaneously provided through the use oftheir burning property. For example, in the case of silicon carbide,carbon dioxide gas and silicate are produced by oxidization reaction asin the following formula (6):

2SiC+2Sr(NO₃)₂→2SrSiO₃+2CO₂+2N₂+O₂  (6)

The carbon dioxide gas and nitrogen thus generated are released in theair bag together with the nitrogen gas, carbon dioxide gas and watervapor produced by the burning of the fuel components, to be effectivelyused for the inflation of the air bag, and the oxygen is used for theburning of the fuel components.

On the other hand, the additionally produced silicate reacts with SrOwhich is produced as a combustion residue by decomposition of strontiumnitrate through the reaction as represented in the above said reactionformulas (3), (5), to form high-viscosity slag that can be easilycollected by the filtering part of the gas generator, as in theabovesaid case. When strontium nitrate is used as the oxidizing agent,the strontium oxide (SrO) produced as the combustion residue reacts withthe carbon gas produced by the formula (6) in accordance with thereaction given by the following formula, to produce strontium carbonate.

SrO+CO₂→SrCO₃  (7)

The strontium carbonate also comes to be a molten state ofhigh-viscosity at around 1,500° C., as in the case of the strontiumsilicate. Accordingly, the strontium carbonate of high-viscosity isformed on surfaces of high-melting particles of the solid strontiumoxide, then allowing the fine particles of the combustion residues tofuse together and aggregate, to form large particles to be easilycollected by the filtering members in the gas generator.

It is preferable that the added amount of these metal carbides is in therange of 0.5 to 20% of the total gas generating agent. With the metalcarbonate of not more than 0.5%, the adequate slag collecting effectscannot be expected, while on the other hand, with the metal carbonate inexcess of 20%, the added amounts of fuel and oxidizing agent arelimited, so that there presents a possible fear of shortage of gasgeneration and incomplete combustion. Preferably, their particlediameter is not more than 5 μm, more preferably, not more than 1 μm, inthe 50% average particle diameter of reference number, because the finerthe particle diameter, the more the effects can be produced.Particularly, when a small amount of fine particulate thereof is addedto the fuel component or oxidizing agent component when pulverized, thefine particulate can act as a consolidation preventing agent for thosepulverized components and also can be dispersed uniformly in theoxidizing agent and the fuel, to ensure uniform reaction for the slag.While the metal carbide can of course be used in combination with theabovesaid metal nitride, the metal carbide is then preferably mixed tobe 0.5-20% in total of the metal carbide and the metal nitride, whencombined.

The basic composition of the gas generating agent of the presentinvention basically comprises the nitrogenous organic compound, theoxidizing agent and the metal nitride or the metal carbide (or both ofthem). To provide further improved slag collecting efficiencies, a slagforming metallic component which can react with the metallic componentof the metal nitride or metal carbide or the oxide thereof to producehigh-viscosity slag may be added in the form of a single substance or acompound. Specifically, the slag collecting and aggregating method issuch that the metal nitride or the metal carbide is allowed to reactwith the oxide of alkaline metal or alkaline earth metal which isproduced by the reaction with the fuel component and the oxidizingagent, to form the high-viscosity slag, and further the slag formingmetallic component which can positively react with the metal nitride ormetal carbide to form the high-viscosity slag is added, whereby theoxide of the alkaline metal or alkaline earth metal is collected andaggregated through the use of the viscosity.

The slag forming metallic components which may be used in the presentinvention include at least one slag forming component selected from thegroup consisting of silicon, boron, aluminum, alkaline metals, alkalineearth metals, transition metals and rare earth metals, which are addedin the form of a single substance or a compound. The metallic componentsof the slag forming metallic components are properly selected withreference to the type of the metal nitride or metal carbide, to form thehigh-viscosity slag. For example, when Fe is used as the metalliccomponent of the metal nitride or metal carbide and Na is selected asthe slag forming metallic component, sodium ferrite having the meltingpoint of 1,347° C. is produced by the following reaction.

Na₂O+2FeO→2NaFeO₂  (8)

Likewise, when Al is used as the metallic component of the nitride orcarbide and Na is selected as the slag forming metallic component,sodium aluminate having the melting point of 1,650° C. is produced bythe following reaction.

Na₂O+Al₂O₃→2NaAlO₂  (9)

When silicon nitride (or silicon nitride) is used as nitride (orcarbide), the slag forming metallic components preferably include atleast one slag forming metallic component selected from the groupconsisting of aluminum (Al), magnesium (Mg), yttrium (Y), calcium (Ca),cerium (Ce) and scandium (Sc). The high-viscosity slag is easily formedby oxides of these metals and silicate originating from silicon nitrideor silicon carbide. Preferably, the slag forming metallic component isadded in the range of 1:9 to 9:1 in a ratio of the slag forming metalliccomponent to the metal nitride or the metal carbide.

There are two methods for adding the slag forming metallic components:one is a method in which the slag forming metallic component is added inthe form of metallic component of the oxidizing agent or metal salt ofnitrogenous organic compound for combustion and the other is a method inwhich the slag forming metallic component is separately added in theform of any compound. Though either of them provides the same slagforming form, not only the slag forming effect but also some othercombined effects should preferably be provided in terms of providingreduced number of raw materials to be added. The method of addinghydrotalcites (hereinafter it is simply referred to as “HTS”) can berecited as a particularly preferable example. The HTS is a compound forwhich the general chemical formula is the same formula as described inGypsum & Lime No. 187 (1983), pages 47-53 and as follows.

[M²⁺ _(1−x)M³⁺ _(x)(OH)₂]^(x+)[A^(n−) _(x/n) .mH₂O]^(x−)

where

M²⁺ represents a bivalent metal including Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺,Cu²⁺ and Zn²⁺;

M³⁺ represents a trivalent metal including Al³⁺, Fe³⁺, Cr³⁺, Co³⁺ andIn³⁺;

A ^(n−) represents an n-valence anion including OH⁻, F⁻, Cl⁻, NO₃ ⁻, CO₃²⁻, SO₄ ²⁻, Fe(CN)₆ ³⁻, CH₃COO⁻, oxalate ion and salicylate ion; and

0<x≦0.33.

The HTS is a porous material having water of crystallization and is veryuseful as a binder for a gas generating agent of nitrogen base organiccompound. The gas generating agent containing the HTS as the binder canprovide a degree of hardness (25-30 Kg) much higher than a degree ofhardness of 10-15 Kg (Monsant type hardness meter) of a pellet of ageneral type of azide base gas generating agent even in a lowpelletization pressure, especially when the nitrogenous organic compoundhaving the tetrazole as its major component is used for the fuel, asdescribed in detail by Japanese Patent Application No. Hei8(1996)-277066 which is the applicant's earlier application. This seemsto be attributed to the HTS having the common property of being liableto absorb moisture to allow the components of the gas generating agentsto be bound firmly. The pellet using this binder keeps itscharacteristic and flammability characteristic unchanged against thethermal shock caused by temperature being raised and fallen repeatedly,thus enabling the pellet to be minimized in deterioration with age afterpractical installation on a vehicle, to be very stable in properties.

Typical of the HTS is the synthetic hydrotalcite (hereinafter it issimply referred to as “synthetic HTS”) for which the chemical formula isMg₆Al₂(OH)₁₆CO₃.4H₂O or the pyroaurite for which the chemical formula isMg₆Fe₂(OH)₁₆CO₃.4H₂O . The synthetic HTS is preferable in terms ofavailability and costs.

Further, for example, the synthetic HTS decomposes as shown in thefollowing reaction formula, so that the HTS produces no harmful gasduring the combustion of the gas generating agent. Also, the reactionitself is an endothermic reaction, and as such can provide anadvantageous effect of reducing a heat release value of the gasgenerating agent when burned, to reduce the combustion temperature.

Mg₆Al₂(OH)₁₆CO₃.4H₂O→6MgO+Al₂O₃+CO₂+12H₂O  (10)

Further, the MgO and Al₂O₃ obtained by the decomposition reaction arethe high-melting oxides of slag forming metallic components, and thesilicate (e.g. SrSiO₃) of metallic components contained in the metalnitride or metal carbide and the MgO produced by the decomposition ofthe synthetic HTS are allowed to react with each other as shown in thefollowing formula, to form an easily filterable, glassy, double salt ofsilicate of magnesium as the slag.

MgO+SrSiO₃→MgO.SrSiO₃  (11)

Also, the decomposition product itself of the synthetic HTS is alsoallowed to form an easily filterable spinel by the slag reaction whichis acid-base reaction shown in the following formula.

MgO+Al₂O₃→MgAl₂O₄  (12)

The HTS is added in the range of 2 to 30% by weight in the total gasgenerating agent composition, when added as the binder. A less than 2%HTS has difficulties in serving as the binder, while on the other hand,a more than 30% HTS causes reduction of an added amount of othercomponents to lead to difficulties in serving as the explosivecomposition. The particle diameter of the HTS is also an importantfactor for production technique. According to the present invention, the50% average particle diameter of a reference number of the binder ispreferably set to be not more than 30 μm. With a particle size of thebinder larger than this, the effect of binding the abovesaid componentsmay be reduced to make it difficult to expect the activity as thebinder, thus there being a fear that a required strength of the formedmember cannot be obtained.

The gas generating agent is generally used in the form of pellet or inthe disk-like form. When the gas generating agent is formed into pelletor a disk-like form, a formability modifying agent may be added for thepurpose of preventing generation of cracks or equivalent in the formedmember. According to the present invention, a 0.01 to 0.5% addition ofwater-soluble polymer compound may be given as the formability modifyingagent. Examples of the water-soluble polymer compounds which may be usedinclude polyvinyl alcohol, polyethylene glycol, polypropylene glycol,polyvinyl ether, polymaleic copolymers, polyethylene imide, polyvinylpyrrolidone, polyacrylamide, sodium polyacrylate and ammoniumpolyacrylate. At least one water soluble polymer is used as required.

For the purpose of providing improved fluidity of powder when the gasgenerating agents are formed into pellets, at least one lubricantselected from the group consisting of stearic acid, zinc stearate,magnesium stearate, calcium stearate, aluminum stearate, molybdenumdisulfide, graphite, atomized silica and boron nitride may be added inthe range of 0.1 to 1% of the total gas generating agent. This canprovide further improved formability of the gas generating agent.

The gas generating agents thus formed may be heat-treated at 100 to 120°C. for about 2 to about 24 hours after formed, to thereby produce theformed products of the gas generating agents which are resistant todeterioration with age. The heat-treatment is very effectiveparticularly for enduring harsh conditions such as a 107° C.×400 hrs.condition. The heat-treatment for less than 2 hours is insufficient andthat for more than 24 hours will be of meaningless, for the reason ofwhich the heat-treatment time should be selected from the range of 2 to24 hours, preferably 5 to 20 hours. Also, the heat-treatment at lessthan 100° C. is not effective and that at more than 120° C. may causedeterioration rather than improvement, for the reason of which theheat-treatment temperature should be selected from the range of 100 to120° C., preferably 105 to 115° C.

Next, description on the preferable combination of the components of thepresent invention will be given. First of all, preferable as fuelcomponents are cyclic nitrogen compounds which are stable and safematerials, having high proportion of an atom of nitrogen in themolecular structure such that they are allowed to decompose to release alarge amount of nitrogen gas and also having the effect of inherentlyrestraining production of harmful carbon monoxide. Particularlypreferable is 5-aminotetrazoles (5-ATZ). Preferable as the oxidizingagent is nitrate having the function of restraining production of NOx,and particularly preferable is strontium nitrate which produces aneasily collectable, high-viscosity slag, in consideration of thecombined use with the metal nitride or metal carbide. The content of the5-ATZ is preferably in the range of 20 to 50% and that of the strontiumnitrate is preferably in the range of 30 to 70%. With less than 20%5-ATZ, an amount of gas generated is reduced, so that there is apossible fear of causing an inflating failure of the air bag. On theother hand, with more than 50% 5-ATZ, the content of the strontiumnitrate of the oxidizing agent is reduced to cause incomplete combustionand thus produce a possible fear of generation of a large amount ofharmful CO gas. Also, with the content of less than 30% strontiumnitrate, insufficient oxidization power is provided to cause incompletecombustion of the 5-ATZ, thus presenting a possible fear of generationof a large amount of harmful CO gas. On the other hand, with more than70% strontium nitride, an amount of gas generated is lacked due to lackof fuel, then arising a possible fear of causing an inflating failure ofthe air bag.

Silicon nitride is preferable as the metal nitride, and silicon carbideis preferable as the metal carbide. This is because silicon content isallowed to react with strontium oxide produced from strontium nitrate inthe process of combustion or metallic components contained in the HTSadded as the binder, to form easily collectable, high-viscosity silicateor double salt thereof. The added amount of silicon nitride or siliconcarbide is preferably in the range of 0.5 to 20%. With a less than 0.5%silicon nitride or silicon carbide, a generation rate of theslag-reaction is reduced, so that MgO or Al₂O₃, which are high-meltingoxides produced from the strontium oxides or the HTS, may be released inthe gas released into the air bag without being fully collected, tocause the burning of the air bag. On the other hand, with a more than20% silicon nitride or silicon carbide, the content of 5-ATZ of the fuelcomponent and of strontium nitrate of the oxidizing agent may be reducedto cause possible incomplete combustion for lack of an amount of gasgenerated or for lack of oxidizing agent.

Next, most preferable as the binder for binding the particulate mixturefor the forming is the synthetic HTS that can produce the high-meltingoxides of MgO and Al₂O₃. They causes the slag reaction with siliconnitride or silicon carbide in the combustion process, to produce thedouble salt of the high-viscosity silicate that is easily collected bythe filtering part of the gas generator. The added amount of thesynthetic HTS is preferably in the range of 2 to 10%. With a less than2% synthetic HTS, a low degree of effectiveness of the binder isprovided, while with a more than 10% synthetic HTS, the content of fueland oxidizing agent may be reduced to cause the abovesaid detrimentaleffects. Further, it is needless to say that since the synthetic HTShave the effect of forming the high-viscosity slag by reaction with themetal nitride or metal carbide, as aforementioned, the slag reactionshould also be considered to select the optimum range according to theamount of metal nitride or metal carbide added.

EXAMPLES

Further detailed description of the present invention will be given withreference to Examples below. It is to be noted that % used in theexamples all indicate weight %.

Example 1

33.5% 5-ATZ used as the fuel component, 63.0% strontium nitrate used asthe oxidizing agent and 3.5% silicon nitride used as the slag formingagent were dryblended with a V-type stirring machine. Before thestirring, impalpable powders of the silicon nitride (0.2 μm in the 50%average particle diameter of the reference number) were added in advanceto the 5-ATZ and the strontium nitrate by amounts that were nearlyproportionally allotted corresponding to their weights. Then, themixture was pulverized to about 10 μm in the 50% average particlediameter of the reference number. The mixed powders were wet-kneaded forgranulation in a rotary mixer, spraying polyvinyl alcohol solution as aformability modifying agent, to be formed into granules having aparticle diameter of not more than 1 mm. The amount of polyvinyl alcoholsolution then sprayed was 0.05% of the total mixture. After the granuleswere heated and dried, 0.2% zinc stearate of the total mixture wasfurther added thereto and stirred, and the resulting mixture waspress-formed with a rotary type tablet making apparatus to obtain thegas generating pellets of 5 mm in diameter, 2 mm in thickness and 88 mgin weight. Then, the pellets thus obtained were heat-treated at 110° C.for 10 hours.

46 g of the pellets thus obtained were loaded in a test-use gasgenerator 1 having the structure shown in FIG. 1. The test-use gasgenerator 1 comprises a central ignition chamber 7 placing therein anignitor 2 and a transfer charge 3; a combustion chamber 8 providedaround the ignition chamber and packing therein the gas generatingagents 4; and a cooling/filtering chamber 9 provided outside of thecombustion chamber and disposing therein a metallic filter 5. Thecombustion gas is exhausted outside from gas exhausting holes 6 in ahousing, passing through the cooling/filtering chamber 9. A 60 litertank test was carried out by use of the gas generator 1. In this test,the gas generator placed in a high pressure vessel having an internalvolume of 60 liter is put in action to release the gas in the vessel,and changes of the internal pressure with time as shown in FIG. 2 andthe amount of slag flown into the vessel are measured. The test resultsof the 60 liter tank test are shown as TABLE 1 in FIG. 3.

In TABLE 1, P₁ represents a maximum range pressure in the vessel (Kpa);t₁ represents the time before the start of operation of the gasgenerator from the power supply to the ignitor 2 (ms:millisecond); andt₂ represents a required time (ms) for the pressure to reach P₁ afterthe operation of the gas generator. The amount of slag flown out isexpressed by weight (g) of solid residue exhausted from the gasexhausting holes 6 and collected in the vessel. Further, the quantity(ppm) of carbon monoxide (CO) and nitrogen oxides (NOx including NO andNO₂) cited as a typical gas that exerts an influence upon a human bodywas determined by an analysis of the gas accumulated in the vessel afterthe operation of the gas generator being conducted by use of aprescribed gas indicator tube.

Example 2

30.8% 5-ATZ, 65.7% strontium nitrate and 3.5% silicon carbide used asthe metal carbide were dryblended with the V-type stirring machine.Before the stirring, impalpable powders of the silicon carbide (0.4 μmin the 50% average particle diameter of the reference number) were addedin advance to the 5-ATZ and the strontium nitrate by amounts that werenearly proportionally allotted corresponding to their weights. Then, thepowder thus mixed was pulverized to about 10 μm in the 50% averageparticle diameter of the reference number. The mixed powders werewet-kneaded for granulation in the rotary mixer, spraying polyvinylalcohol solution as a formability modifying agent, to be formed intogranules having a particle diameter of not more than 1 mm. The amount ofpolyvinyl alcohol solution then sprayed was 0.05% of the total mixture.After the granules were heated and dried, zinc stearate of 0.2% of thetotal mixture was further added thereto and stirred, and the resultingmixture was press-formed with the rotary type tablet making apparatus toobtain the gas generating pellets of 5 mm in diameter, 2 mm in thicknessand 88 mg in weight. Then, the pellets thus obtained were heat-treatedat 110° C. for 10 hours.

46 g of the pellets thus obtained were loaded in the gas generator ofFIG. 1 as in Example 1, and the same test was conducted. The resultsobtained are shown as TABLE 1 in FIG. 3.

Example 3

As is the case of Example 1, the mixture comprising 32.0% 5-ATZ, 59.9%strontium nitrate, 3.6% silicon nitride and 4.5% synthetic HTS wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon nitride were added in advance and which were pulverizedto about 10 μm in the 50% average particle diameter of the referencenumber. The mixture underwent the wet kneading granulation process inthe same way as in Example 1, to produce the gas generating pellets of 5mm in diameter, 2 mm in thickness and 88 mg in weight. Then, the pelletsthus produced were heat-treated in the same manner. The silicon nitrideand the synthetic HTS used here were 0.8 μm and 10 μm in the 50% averageparticle diameter of the reference number, respectively. 46 g of thepellets thus obtained were loaded in the gas generator of FIG. 1 as inExample 1 and the same test was conducted. The results obtained areshown as TABLE 1 in FIG. 3.

Example 4

As is the case of Example 2, the mixture comprising 30.0% 5-ATZ, 61.9%strontium nitrate, 3.6% silicon carbide and 4.5% synthetic HTS wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon carbide were added in advance and which were pulverizedto about 10 μm in the 50% average particle diameter of the referencenumber. The mixture underwent the wet kneading granulation process inthe same way as in Example 2, to produce the gas generating pellets of 5mm in diameter, 2 mm in thickness and 88 mg in weight. Then, the pelletsthus produced were heat-treated in the same manner. The silicon carbideand the synthetic HTS used here were 0.4 μm and 10 μm in the 50% averageparticle diameter of the reference number, respectively. 46 g of thepellets thus obtained were loaded in the gas generator of FIG. 1 as inExample 1 and the same test was conducted. The results obtained areshown as TABLE 1 in FIG. 3.

Example 5

As is the case of Example 1, the mixture comprising 31.0% 5-ATZ, 63.0%strontium nitrate, 3.4% silicon nitride and 2.6% aluminum nitride wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon nitride and aluminum nitride were added in advance andwhich were pulverized to about 10 μm in the 50% average particlediameter of the reference number. The mixture underwent the wet kneadinggranulation process in the same way as in Example 1, to produce the gasgenerating pellets of 5 mm in diameter, 2 mm in thickness and 88 mg inweight. Then, the pellets thus produced were heat-treated in the samemanner. The silicon nitride and the aluminum nitride used here were 0.8μm and 1.0 μm in the 50% average particle diameter of the referencenumber, respectively. 46 g of the pellets thus obtained were loaded inthe gas generator of FIG. 1 as in Example 1 and the same test wasconducted. The results obtained are shown as TABLE 1 in FIG. 3.

Example 6

As is the case of Example 1, the mixture comprising 31.0% 5-ATZ, 63.0%strontium nitrate, 3.4% silicon carbide and 2.6% of aluminum nitride wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon carbide and impalpable powders of the aluminum nitridewere added in advance and which were pulverized to about 10 μm in the50% average particle diameter of the reference number. The mixtureunderwent the same process as in Example 1, to produce the gasgenerating pellets of 5 mm in diameter, 2 mm in thickness and 88 mg inweight. Then, the pellets thus produced were heat-treated in the samemanner. The silicon carbide and the aluminum nitride used here were 0.8μm and 1.0 μm in the 50% average particle diameter of the referencenumber, respectively. 46 g of the pellets thus obtained were loaded inthe gas generator of FIG. 1 as in Example 1 and the same test wasconducted. The results obtained are shown as TABLE 1 in FIG. 3.

Example 7

As is the case of Example 1, the mixture comprising 32.3% 5-ATZ, 61.0%strontium nitrate, 3.5% silicon nitride and 3.2% aluminum oxide wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon nitride were added in advance and which were pulverizedto about 10 μm in the 50% average particle diameter of the referencenumber. The mixture was formed into the gas generating pellets of 5 mmin diameter, 2 mm in thickness and 88 mg in weight in the samemanner asin Example 1 . Then, the pellets thus produced were heat-treated in thesame manner. The silicon nitride used here was 0.8 μm in the 50% averageparticle diameter of the reference number. 46 g of the pellets thusobtained were loaded in the gas generator of FIG. 1 as in Example 1 andthe same test was conducted. The results obtained are shown as TABLE 1in FIG. 3.

Example 8

As is the case of Example 1, the mixture comprising 32.3% 5-ATZ, 61.0%strontium nitrate, 3.5% silicon carbide and 3.2% aluminum oxide wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon carbide were added in advance and which were pulverizedto about 10 μm in the 50% average particle diameter of the referencenumber. The mixture was formed into the gas generating pellets of 5 mmin diameter, 2 mm in thickness and 88 mg in weight in the same manner asin Example 1 . Then, the pellets thus produced were heat-treated in thesame manner. The silicon carbide used here was 0.8 μm in the 50% averageparticle diameter of the reference number. 46 g of the pellets thusobtained were loaded in the gas generator of FIG. 1 as in Example 1 andthe same test was conducted. The results obtained are shown as TABLE 1in FIG. 3.

Comparative Example 1

As is the case of Example 1, the mixture comprising 35.8% 5-ATZ, 62.2%strontium nitrate and 2.0% silicon dioxide was prepared using 5-ATZ andstrontium nitrate to which impalpable powders of the silicon dioxidewere added in advance and which were pulverized to about 10 μm in the50% average particle diameter of the reference number. The mixture wasformed into the gas generating pellets of 5 mm in diameter, 2 mm inthickness and 88 mg in weight in the same manner as in Example 1 . Then,the pellets thus produced were heat-treated in the same manner. Thesilicon dioxide used here was 0.014 μm in the 50% average particlediameter of the reference number. 46 g of the pellets thus obtained wereloaded in the gas generator of FIG. 1 as in Example 1 and the same testwas conducted. The results obtained are shown as TABLE 1 in FIG. 3.

Comparative Example 2

As is the case of Example 1, the mixture comprising 34.1% 5-ATZ, 59.3%strontium nitrate, 1.8% silicon dioxide and 4.8% synthetic HTS wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon dioxide were added in advance and which were pulverizedto about 10 μm in the 50% average particle diameter of the referencenumber. The mixture was formed into the gas generating pellets of 5 mmin diameter, 2 mm in thickness and 88 mg in weight in the same manner asin Example 1 . Then, the pellets thus produced were heat-treated in thesame manner. The silicon dioxide used here was 0.014 μm in the 50%average particle diameter of the reference number. 46 g of the pelletsthus obtained were loaded in the gas generator of FIG. 1 as in Example 1and the same test was conducted. The results obtained are shown as TABLE1 in FIG. 3.

Comparative Example 3

As is the case of Example 1, the mixture comprising 33.2% 5-ATZ, 57.8%strontium nitrate, 4.5% silicon dioxide and 4.5% synthetic HTS wasprepared using 5-ATZ and strontium nitrate to which impalpable powdersof the silicon dioxide were added in advance and which were pulverizedto about 10 μm in the 50% average particle diameter of the referencenumber. The mixture was formed into the gas generating pellets of 5 mmin diameter, 2 mm in thickness and 88 mg in weight in the same manner asin Example 1 . Then, the pellets thus produced were heat-treated in thesame manner. The silicon dioxide used here was 0.014 μm in the 50%average particle diameter of the reference number. 46 g of the pelletsthus obtained were loaded in the gas generator of FIG. 1 as in Example 1and the same test was conducted. The results obtained are shown as TABLE1 in FIG. 3.

As seen from TABLE 1 , the quantities of slag flown out are in the rangeof 4.0 to 4.5 g in all Examples 1 to 8, while on the other hand, largequantities of slag in excess of 11 g are flown out in ComparativeExamples 1 and 2 in which about 2% silicon dioxide was added. It can beunderstood from this that the metallic components of the metal nitrideor metal carbide in the gas generating agent of the present inventioncan form the high-viscosity slag to collect the slag in an effectivemanner.

In Comparative Example 3 in which an added amount of silicon dioxide isincreased, the amount of slag flown out was slightly improved to be notmore than 10 g, while the time t₂ required for the pressure to reach P₁,or the burning rate, was reduced and, resultantly, the value of P₁ wasalso lowered. In view of this, the amount of slag flown out and theburning rate are in an antinomy relation, so that it was difficult toperform optimizations of the both. On the other hand, though the gasgenerating agents of the present invention using the metal nitride ormetal carbide shows similarity in slag forming reaction to the known oneadding thereto the silicon dioxide, the metal nitride or metal carbideentails the generation of gas in the combustion process and generatesthe heat of reaction resulting from oxidation reaction, and as suchprobably promotes improvement of the burning rate and the maximum rangepressure.

Further, the present invention shows the amounts of generated harmful COgas of about 2,000 to 3,500 ppm, whereas Comparative Examples show 8,000ppm higher than twice as much as in the present invention. It seems thatthis is because since the reaction in which the metal nitride or metalcarbide used in the present invention reacts with oxygen to producemetallic oxides and nitrogen gas or carbonic acid gas is an exothermicreaction, the combustion temperature in the gas generator is increasedso that the generation of CO can be restrained. From the fact that themaximum range pressure P₁ of the present invention shows a relativelyhigh value, as compared with Comparative Examples, it is presumed thatthe reaction temperature is increased. In this connection, as thereaction temperature increases, the amounts of generated NOx increase ingeneral, but contrarily the present invention shows relatively lowvalues. In the present invention, it is presumed that the metalliccomponents supplied as the metal nitride or metal carbide consumeoxygen, so that the oxygen to react with the nitrogen gas is reduced.

As obvious from the explanation above, it will be understood that themetal nitrides or metal carbides used in the gas generating agents ofthe present invention provide outstanding differences in operation andeffect, as compared with the generally used silicon dioxides.

As mentioned above, according to the present invention, the followingoutstanding effects can be achieved.

The metal nitride or metal carbide used as the slag forming agent isadded to non-azide gas generating agent including nitrogenous organiccomponent and the oxidizing agent as its major components, so that themetallic component of the metal nitride or metal carbide is allowed toreact with harmful metallic oxide which is produced mainly from theoxidizing agent, to produce the high-viscosity slag. This enables theslag to be easily collected by the filters placed in the gas generatorto suppress the outflow of the slag, thus providing improved safety ininflating the air bag.

Also, the compound containing the slag forming metallic component thatis allowed to react with the metallic component of metal nitride ormetal carbide or oxide thereof to produce the high-viscosity slag isadded separately, so that even when atomized high-melting metallicoxides are generated, high-viscosity slag layers are formed on theirsurface layers by the slag reaction on the surfaces and are allowed tofuse and aggregate together to result in the combustion residues thatcan be easily filtered by the filters. Thus, the outflow of the harmfulmetallic oxides can be suppressed.

Also, the metal nitride or metal carbide decomposes to produce nitrogengas or carbonic acid gas, and the gas components are useful for andcontribute to the inflation of the air bag. Thus, the content of thenitrogenous organic compound as the fuel component can be saved, and assuch can provide the contribution to the reduction of size and weight ofthe gas generator.

Also, since the reaction in which the metal nitride or metal carbide isburned in the presence of oxygen is an exothermic reaction, thecombustion temperature in the gas generator is increased so that thegeneration of CO gas can be restrained and also higher pressure gas canbe released into the air bag. Thus, the inflation of the air bag canfurther be ensured.

CAPABILITIES OF EXPLOITATION IN INDUSTRY

As mentioned above, the gas generating agent of the present inventionprovides reduced generation of harmful gas and besides increasedcapability of collecting the slag, and thus is very useful for use inthe gas generator of an automobile air bag system.

What is claimed is:
 1. A gas generating agent for an air bag comprising a fuel component, which is a nitrogenous organic compound, and an oxidizing agent as the major components of the gas generating agent, and at least 2.6% of silicon nitride functioning as consolidation preventing agent for at least either of said fuel component or said oxidizing agent, a metallic component being in said fuel component compound or in said oxidizing agent and said metal nitride further being able to react in a combustion process to form high-viscosity slag with said metallic component, further, containing an additional slag forming metallic component that can react with a metallic component of said metal nitride or oxide originating from the metal nitride in a combustion process to form said high-viscosity slag, the slag forming metallic component being an element or a compound.
 2. A gas generating agent for an air bag as set forth in claim 1, wherein said silicon nitride as the consolidation preventing agent for at least either of said fuel component and said oxidizing agent is in the form of impalpable powder.
 3. A gas generating agent for an air bag as set forth in claim 1, wherein said silicon nitride is added in the range of 2.6% to 20 weight % of the total gas generating agent.
 4. A gas generating agent for an air bag as set forth in claim 1 or 3, wherein said slag forming metallic component is at least one slag forming metallic component selected from the group consisting of silicon, boron, aluminum, alkaline metals, alkaline earth metals, transition metals and rare earth metals.
 5. A gas generating agent for an air bag as set forth in claim 1, wherein said additional slag forming metallic component is added thereto in the form of a hydrotalcite for which the general chemical formula is: (M²⁺ _(1−x)M³⁺ _(x)(OH)₂)^(x+)(A^(n−) _(x/n) .mH₂ O)^(x−) where M²⁺ represents bivalent metal including Mg²⁺, Mn²⁺, Fe²⁺, CO²⁺, Ni²⁺, Cu²⁺ and Zn²⁺; M³⁺ represents bivalent metal including Al³⁺, Fe³⁺, Cr³⁺, CO³⁺ and In³⁺; A ^(n−) represents an n-valence anion including OH⁻, F⁻, Cl⁻, NO₃ ⁻, CO₃ ²⁻, SO₄ ²⁻, Fe(CN)₆ ³⁻, CH₃COO⁻, oxalate ion and salicylate ion; and 0<x≦0.33.
 6. A gas generating agent for an air bag as set forth in claim 5, wherein said hydrotalcites is synthetic hydrotalcite for which the chemical formula is Mg₆Al₂(OH)₁₆CO₃.4H₂O, or pyroaurite for which the chemical formula is Mg₆Fe₂(OH)₁₆CO₃.4H₂O.
 7. A gas generating agent for an air bag as set forth in claim 6, wherein said synthetic hydrotalcite or said pyroaurite is added in the form of a compound including a component both as a binder for said gas generating agent composition and as said slag forming metallic component.
 8. A gas generating agent for an air bag as set forth in claim 5, wherein said synthetic hydrotalcite or said pyroaurite is added in amount of 2 to 10 weight % of the total gas generating agent.
 9. A gas generating agent for an air bag as set forth in claim 1 or 3, wherein said nitrogenous organic compound is at least one nitrogenous organic compound selected from the group consisting of tetrazole, aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole, nitroaminotetrazole, triazole, nitroguanidine, aminoguanidine, triaminoguanidine nitrate, dicyanamido, dicyandiamido, carbohydrazide, hydrazocarbonamido, azodicarbonamide, oxamide and ammonium oxalate or their salts of alkaline metals, alkaline earth metals or transition metals.
 10. A gas generating agent for an air bag as set forth in claim 1 or 3, wherein said nitrogenous organic compound is a cyclic nitrogen compound.
 11. A gas generating agent for an air bag as set forth in claim 10, wherein said cyclic nitrogen compound is at least one cyclic nitrogen compound selected from the group consisting of tetrazole, aminotetrazole, bitetrazole, azobitetrazole, nitrotetrazole, nitroaminotetrazole, triazole or their salts of alkaline metals, alkaline earth metals or transition metals.
 12. A gas generating agent for an air bag as set forth in claim 1 or 3, wherein said oxidizing agent is at least one oxidizing agent selected from the group consisting of nitrates of alkaline metal or alkaline earth metals, chlorates of alkaline metals or alkaline earth metals, perchlorates of alkaline metals or alkaline earth metals and ammonium nitrates.
 13. A gas generating agent for an air bag as set forth in claim 1 or 3, wherein a water-soluble polymer compound is added as a formability modifying agent in amount of 0.01 to 0.5 weight % of the total gas generating agent composition to said gas generating agent composition.
 14. A gas generating agent for an air bag as set forth in claim 13, wherein said water-soluble polymer compound is at least one water-soluble polymer compound selected from the group consisting of polyvinyl alcohol, polypropylene glycol, polyvinyl ether, polymaleic copolymers, polyethylene imide, polyvinyl pyrrolidone, polyacrylamide, sodium polyacrylate and ammonium polyacrylate.
 15. A gas generating agent for an air bag as set forth in claim 1 or 3, wherein 0.01 to 1 weight % lubricant is added to said gas generating agent composition and is molded in a predetermined form.
 16. A gas generating agent for an air bag as set forth in claim 15, wherein said lubricant is at least one lubricant selected from the group consisting of stearic acid, zinc stearate, magnesium stearate, calcium stearate, aluminum stearate, molybdenum disulfide and graphite.
 17. A gas generating agent for an air bag comprising 20 to 50 weight % 5-aminotetrazole as a fuel component; 30 to 70 weight % strontium nitrate as an oxidizing agent; and 0.5 to 20 weight % silicon nitride as a slag forming agent; and 2 to 10 weight % synthetic hydrotalcite both as a binder and as a high-viscosity slag forming metallic compound.
 18. A gas generating agent for an air bag comprising 20 to 50 weight % 5-aminotetrazole as a fuel component; 30 to 70 weight % strontium nitrate as an oxidizing agent; and 0.5 to 20 weight % silicon nitride as a slag forming agent, wherein a slag forming metallic compound comprising at least one slag forming metal selected from the group consisting of aluminum, magnesium, yttrium, calcium, cerium and scandium is further mixed in the range of 1:9 to 9:1 in a ratio of said silicon nitride to said slag forming metallic compound.
 19. A gas generating agent for an air bag as set forth in claim 18, wherein said slag forming metallic compound is at least one of oxide, hydroxide, nitride, carbide, carbonate and oxalate of said slag forming metal.
 20. A gas generating agent for an air bag as set forth in claim 18, wherein said slag forming metallic compound is synthetic hydrotalcite.
 21. A gas generating agent for an air bag as set forth in claim 5, comprising 32% 5-amino triazole, 59.9% strontium nitrate, 3.6% silicon nitride and 4.5% synthetic hydrotalcite.
 22. A gas generating agent for an air bag as set forth in claim 19, wherein said slag forming metallic compound is aluminum nitride or aluminum oxide. 